how to disable auto smoothing by default in 2.74
You cannot (well, not from UI or other 'user-land' ways). Note however that 'autosmooth' here is a bit of a weak name, since it actually means you are using (custom) normals as defined by the .obj, instead of auto-computed ones by Blender…

Now, if you really want to disable that by default, you'll have to open addons/io_scene_obj/import.py in your Blender installation, search for me.use_auto_smooth = True (should be around line 657 currently), and replace it by me.use_auto_smooth = False (or just comment it by adding a # in front of that line).

But again, don’t think you want to do that, at least I do not see why you would…